1920-1974 Modiolus modiolus in small, mid-tidal rock pools at Penrhyn Bay, North Wales dataset https://portal.medin.org.uk/portal/start.php?tpc=010_1f822870ba02d4834cd6664fb64c7809 Modiolus modiolus records from Penrhyn bay, North Wales. Taken from observations of Modiolus distribution within the bay over a number of years. The author notes; "The shore at Penrhyn Bay, North Wales is strewn with glacial boulders. Many are of limestone, their surfaces often pitted and hollowed, the hollows often retaining water at low tide. On one particular boulder, at approximately mid-tide level, two such rock pools have been inhabited by Modiolus modiolus (L.) continuously, or almost so, since the early 1920s, although the species has only once been found elsewhere on this shore, in similar rock pools nearby." 19771231 19200101